Image quality in magnetic resonance imaging (MRI) is considerably affected by motion. MRI scans may acquire data over a prolonged period of time. Due to the time it takes to perform the scan, MRI scans may capture many different types of movements, such as involuntary movements, cardiac and respiratory motion, vessel pulsation, and blood flow among other movements. Motion induced effects, e.g. artifacts, in MRI potentially include a combination of blurring of sharp contrast or object edges, ghosting originating from moving structures, signal loss due to spin dephasing or undesired magnetization evolution, or appearance of undesired strong signals among other artifacts. Motion is one of the most common sources of artifacts in MRI. The artifacts may lead to misinterpretations in the images and a subsequent loss in diagnostic quality.
Many techniques are used to prevent or suppress motion artifacts. If motion can be avoided, then the effects may be avoided. Rigid structures, sedation, and breath-holding among other techniques may be used to prevent movement. Faster acquisition may also be used to shorten the acquisition time of magnetic resonance (MR) data and therefore suppress the motion artifacts. Motion artifacts may also be removed or corrected when processing the MRI scan data. MRI navigators or markers may be used that infer or identify the motion of the subject using measurements or identifiers in the MRI data.
These techniques provide a first line of defense against motion artifacts but do not completely prevent artifacts from occurring. Additionally, the preventive techniques may be performed when acquiring the image data. When subsequently viewed, any motion artifacts may be unable to be corrected or may require performing an additional scan (for example, requiring a patient to make an additional trip to a medical facility and undergo another scanning procedure).